Chain cutter type excavator and ditch excavating method

ABSTRACT

An excavator is provided with a box type casing including a pair of rotary cutters mounted on the bottom portion of the casing; blades provided at the outer periphery of the cutters provide excavating action with soil so excavated being discharged through a discharging tube having a sucking port around the rotary cutters; further provision being made for slide cutters on the periphery of the casing. In operation the inter action of the rotary cutters provides discrete and alternate ditch bores whereafter the areas between the ditch bores are excavated to form a ditch of desired length and width.

United States Patent n 1 Endo et a1.

[ 1 Jan. 16, 1973' [54] CHAIN CUTTER TYPE EXCAVATOR AND DITCH EXCAVATING METHOD [75] Inventors: Masaaki Endo, Ohmiya; Mituo Miura; Mamoru Shinozaki, both of Tokyo, all of Japan [73] Assignee: Takenaka Komuten Cornpany, Ltd.,

- Higashi-ku, Osaka-fu, Japan [22] Filed: Dec. 4, 1970 [21] Appl. No.: 95,037

[30] Foreign Application Priority Data Dec. 13, 1969 Japan ..44/100752 [52] US. Cl. ..l75/66, 37/80, 37/83, 37/195,175/89, 175/91 [51] Int. Cl ..E02f /06, E21b 11/06 [58] Field of Search. ..175/57, 65, 67, 89, 90, 91; 37/80 R, 83, DIG. 6, 80, 59, 66, 67, 195

[56] References Cited UNITED STATES PATENTS 2,762,136 9/1956 Bell ..37/67 867,536 /1907 Rochford et al 175/89 2,849,213 8/1958 Failing ..l/2l 3 2,643,096 6/1953 Bates ..37/ R X 3,310,952 3/1967 Veder ..37/l X Primary Examiner-Ernest R. Purser Attorney-Fidelman, Wolffe, Leitner & Hiney [5 7] ABSTRACT An excavator is provided with a box type casing including a pair of rotary cutters mounted on the bottom portion of the casing; blades provided at the outer periphery of the cutters provide excavating action with soil so excavated being discharged through a discharging tube having a sucking port around the retary cutters; further provision being made for slide cutters on the periphery of the casing. in operation the inter action of the rotary cutters provides discrete and alternate ditch bores whereafter the areas between the ditch bores are excavated to form a ditch of desired length and width.

7 Claims, 17 Drawing Figures PATENTEDJAH 16 1975 sum 3 [IF 5 CHAIN CUTTER TYPE EXCAVATOR AND DITCH EXCAVATING METHOD The present invention relates to a rotary cutter type excavator, and more particularly to such an excavator wherein rotary cutters rotatable in opposite directions at the same speed are provided at the tip ends of a box type casing having its bottom side opened and so constructed that excavated soil is discharged on the ground with muddy water, and to an excavation method using such an excavating a rectangular, deep ditch or bore with high efficiency and stability.

The excavator of the present invention is intended to be used in an excavation method wherein ground stabilizing solution (sometimes referred to as muddy water) such as bentnite solution is used, and provided with an excavation mechanism for muddy water caused by the solution. The peripheral walls of the rotary cutter form an excavation chamber (excavation section) which is substantially completely closed by casing or the like. Liquid (muddy water) in the excavation chamber and the external liquid (i.e. the stabilizing liquid filled into the excavated ditch) are isolated and separated to suppress intercommunication of both liquids and mobility of the stabilizing liquid so that they are maintained in substantially static state thereby the stabilizing liquid functions effectively to stabilize the ditch walls.

The second feature of the present invention is a construction in which an excavator mechanism with rotary cutters and a soil discharging mechanism for discharging excavated soil including muddy water by means of fluid carrier system are completely separated and independent to fully accomplish the first object of the present invention and to double the excavating capability.

The third feature of the present invention is that the excavation mechanism employs a rotary cutting mechanism in which a pair of rotary cutters are rotated in opposite directions, thereby excavating torques are balanced and deflection of the excavator is eliminated and excavation accuracy is increased, permitting stable, noiseless and vibration-free excavation.

The soil discharging mechanism is characterized in that an upward nozzle is provided just below the opening of the soil discharging tube formed in bell mouth shape, high speed jet from the nozzle to transport the mudy water including the excavated soil to an area in the opening of the soil discharging tube where it canbe sucked, and in that by the addition of the energy of the jet the suckable area of the soil discharging mechanism may be expanded to provide a sufficiently large soil discharging capability.

The other feather is that the penetration force of the excavator (especially frictional resistance and excavating force) is reduced by the use of slide cutter, and excavation of the ditch is effected such that a rectangular ditch having a geometry substantially equal to the lon-v are how we should" efficiently excavate the ground of different types of soil, how we should discharge the excavated soil on the ground rapidly and how should maintain the stability of the excavated ditch until the drive of the concrete. One of the solutions is a muddy water excavation method using ground stabilizing solution such as bentnite solution.

It is a recent trend to use the underground continuous wall not only as water suppress wall but also as earthquake resisting wall to be used in future or undergro und construction wall. For the works in or near the city many functional restrictions are imposed on the excavator from the viewpoint of prevention of public hazard such as vibration and noise.

In the past, for the machines to be used to excavate such ditch or the like many apparatus have particular functions depending upon the kind of soil, the depth of the ditch or ambient conditions (external conditions) have been developed, but, in general, their excavation section have functions of both excavation mechanism and soil discharging mechanism, as typically seen in a shovel excavator. Therefore, their excavation operation is not continuous and the excavation capability is extermely low. The biggest problem in the above type of machine is that since the excavation section moves violently in the stabilizing liquid, it creates eddy flow or motion of flow in the stabilizing liquid, thus preventing sufficient stabilizing operation on the ditch wall. Furthermore, since the excavation of this type is effected not by cutting the ground but by destroying the ground by the impact force of the excavation section and tearing off the ground soil, big noise and vibration are produced which in turn becomes a cause of public hazard.

It may be concluded that the requirements for an ideal excavator are as fellows:

i. In continuously excavating a deep ditch having rectangular cross-section which may be used to function as frame for a continuous underground wall, it must be capable of excavating a ditch of rectangular cross-section from the beginning with precisely controlled predetermined size.

ii. It must be of the type of excavation and soil discharge which will not destroy ditch wall. Namely, the stabilization of the ditch wall by the bentnite solution should, of course, be performed, and the excavation and soil discharge operations should not cause the motion of the solution and should not lower the stabilization ability for the ditch wall. For this end, it is preferable that the excavation mechanism and the soil discharging mechanism are independent from each other and soil discharging is effected by means of suction or ejection using a fluid.

iii. it must be an excavation mechanism-which'does not convey violation or impact to the surrounding ground.

iv. Accordingly, it must be a machine which does v not, of itself, produce violation and noise (for this purpose it seems that a rotary cutter type is ideal).

v. It must be a machine capable of rapidly discharging the excavated soil onto the ground in continuous and high efficiency operation.

vi. It should allow a sufficiently high accuracy of work. As for the vertical accuracy, it is necessary to the extent that it maintains the accuracy required for structary cutter, FIGS. 8A, 8B, 8C and 8D show newly developedf (i) through '(vii). It will be more fully described in conjunction with the preferred embodiments illustrated in the accompanying drawings; in which;

FIG. 1 is a side cross-sectional view illustrating the details of the structure of the excavator in accordance with the present invention;

FIG. 2 is a front sectional-view of the same excavator;

FIG. 3 is an illustration of soil discharging mechanism using jet flow;

FIG. 4 is a developed view showing the arrangement of the excavating blades of a rotary cutter;

FIG. 5 is a diagram showing the relationship between the excavator and the associated apparatus and facilities required for the operation of the excavator;

FIGS. 6A, 6B and 6C illustrate the simplest way of excavation using the excavator of the present invention;

FIGS. 7A and 78 illustrates the possibility by the roexcavation system for rotary cutter type excavation;

and r FIGS. 9A 9C illustrate an example of excavation operation.

In the following description, the excavator of the present invention will be explained first by each of its major parts, that is, a main frame, a rotary cutter, drive means, soil discharging mechanism and slide cutter, and then the procedure of the excavation will be explained together with the facilities for operating the excavator.

A casing 11 of a main frame has I-shaped steels inrigidity against penetration force and excavation resistance, and it is constructed in box-shape having iron plate applied to its side surfaces. Only the bottom side 'of the box is opened, to which a pair of rotary cutter l4 and 15 are oppositely mounted.

As will be described below, each of the rotary cutters l4 and 15 has mounted on a drum surface, in a predetermined pattern, excavating blades comprising a set of a leading blade 12 and a trailing blade 13. The cutters are rotated in opposite directions at the same speed for cancelling out the excavating torques produced by the cutters to keep the force in balance. The cutters are so constructed that the muddy water including excavated soil is brought to the intermediate of the both cutters.

ln mounting the cutters 14 and 15, a problem will be raised on the structure of bearing, that is, the location of shaft sealing device and bearing for static pressure of the stabilizing liquid which proportionally increases with the depth of the ditch. For example, if thebearing projects outwardly of the outer side of the casing 11, it

'45 corporated thereto to exhibit a sufficient strength and will necessarily interfere with the penetration of the machine On the other hand, if it projects inwardly, the width of the blade of the cutter l4 and 15 becomes too narrow to compare with the width of the casing 1 l and hence many disadvantageswill result. In thepresent in-- The reference numeral 17 designates drive means mounted at a relatively upper position of the casing l 1. In order to rotate the pair of rotary cutters 14 and 15 at a constant equal speed with the same torque, two 'oil pressure motors l8 and '19 are geared with intermediate gears 20 and 21 to transmit their rotating power to main sprockets 22 and 23 of the output shaft. The drive means 17 is characterized in that, although it is a problem how the shaft sealing device should be constructed for the static pressure of the muddy water since the present machine is the one used in muddy water excavation work, the output shaft of the oil pressure motors 18 and 19 are enclosed by sealing chamber at the side where the effect of the pressure oil is less, in which chambers thegear trains are mounted to trans mit the driving power to the main sprockets 22 and 23, thus permitting a sufficient shaft sealing at the bearing portions of the main sprockets 22 and 23. By way of example, if the depth of the excavated ditch reaches 30 m, thestatic pressure of the muddy water (bentnite solution having specific gravity of 1.07 1.08) reaches about 3.24 kg/cm.

The main sprockets 22 and 23 dr ive intermediate shafts 24 and 25 through roller chains 24a and 25a, and rotary cutters 14 and 15 through other roller chains 26 and 27, via respective power transmission mechanism and under the same operation condition. In order to eliminate the disability of the excavation of the portions corresponding to the width of the roller chains 26 and 27, the excavation blade comprising a set of leading blade 28 and trailing blade 29 is provided to complete a chain cutter structure.

Detailsof the excavating blade will now be described referring to FIG. 4. The leading blade and the trailing blade as herein defined are; the leading blade has narrow blade width and is capable of cutting the ground deeply while the trailing blade has wide blade width and dig the ground which has been digged and made unstable by the leading blade, whereby in excavating the ground is not destroyed but completely out.

As seen from FIGS. 1 and 4, the rotary cutters l4 and 15 have at their center portions sprockets mounted to receive drive power from the oil pressure motor. The excavating blades symmetrically arranged at left and right portions 14a and 14b of the cutter 14 and the chain cutter 26 define overall blade width 11. The excavating blades of the rotary cutter 14 or 15 are arranged for rotational angle of 11/2, and the leading blades 12 and the trailing blades 13 are alternately arranged for each 1r/2 angle. By one revolution of the cutter drum a uniform excavation of the blade width 11 may be formed. On the other hand, the excavating blades of the chain cutters 26 and 27 are arranged such that they are located for each 11/4 angle with respect to the arrangement of the excavating blades of the rotary cutters.

vide highly flattened ditch wall, and at the same time it' pushes away the ground soil toward the rotary cutters 14 and 15 to facilitate the operation of the excavator. Fixed to the slide cutter 30 are beams 32, 32 mounted through windows 31,31 formed on the side of the casing 11, the piston rods of the power cylinders 33, 33 being coupled to the beams to operatively link them.,

The cutting blade 30a of the slide cutter 3.0 is so designed that it has small component of penetration resistance and is capable of cutting mainly by the component of cutting resistance.

According to the present invention, the rotary cutters l4 and 15 are so shaped that they give a constant differential height on the cutting ground and also give a differential height with a constant blade width to provide so-called combined leading blade 30-A and trailing blade 30-B, to thereby permit smooth cutting of the ground. At the same time, the slide cutter 30 surrounds the portions at which the rotary cutter 14 and 15 are located and, together with a cutter casing described below, defines a closed excavating chamber and also functions to shut off the flow of the muddy water in the excavating chamber from the external.

The soil discharging mechanism is finally described. In FIGS. 1 to 3, the reference numerals 34a and 34b designates cutter casings mounted along the blade tip circles of the left and right rotary cutters 14 and 15. They have their center portions restricted to present so-called bell mouth configuration and are connected to a soil discharging tube 8. The cutter casings 34a and 34b are divided between the chain cutters 26 and 27, and the soil discharging tube 8 connected to a suction pump 8a (FIG. 5) is also branched at its lower section to two pipes 8-A and 8-8 of equal diameter which are individually connected to the casings 34a and 34b.

In the FIG. 2 and 3, the reference numerals 35a and 35b designate upward nozzles provided just below the opening of the soil discharging tube 8. The nozzles 35a and 35b are rotated through the rotary cutters l4 and 15 to project high speed jets from the bottom to the muddy water including the excavated soil collected to the center portion, for transport the muddy water to the suckable area of the opening of the soil discharging pipe 8. As seen' from FIGS. 2 and 3, depending upon the structure of the cutter casings 34a, 34b and the soil discharging tube 8, the nozzles 35a and 3517 are mounted separately on a nozzle mount 36 fixedly attached across the casing 11. Connected to the water feeding ports 37 are pipes 7-A and 7-B of equal diameter branched at lower section of an ejection pipe 7 connected to an ejection pump 7a (FIG. 5). The numerals 38 and 39 designates guide vanes for regulaing the flow.

The suckable energy distribution in the opening of the soil discharging tube 8 due to the ability of the sucking pump (FIG. 5) decreases as an inverse function of the distance from the tube opening. Effective soil discharging operation cannot be expected solely by a centrifugal force imported to the muddy water by the rotary cutters 14 and 15. Especially when the depth of the excavated ditch exceeds an effective pump-upstroke of the pump, the effect of the suck approximates to zero.

For simplification, the fluid velocity Vo required to carry the ballast which has not been made muddy can 7 be expressed by the following general formula:

where discharging tube, the effective pump-up-stroke of the sucking pump and. hence suckable area of the opening of the soil discharging tube due to the sucking pump are expanded. I

In the machine of the present invention it may be said that it is a centrifugal force by the rotary cutters l4 and 15 and a jet flow by the nozzles 35a and 35b that provides the above energy.

The function and operation of the jet flow may also be explained as follows; Assuming that Q is a flow rate of the jet flow, Qs is an average flow rate in the soil discharging tube 8 and Qf is a flow rate of the flow rotated by the rotary cutters and flowing into from the periphery of the jet flow, then the equation Qs =Q W Qf is derived in accordance with an experiment.

It should be particularly noted that if Q in theabove equation increases gradually, there exists a range where Qs abruptly increases (it is considered that this may be explained from the Bemoullis energy equation) and Qf increases correspondingly. Namely, since the fluid flowing in from the periphery of the jet flow is the muddy water including the excavated soil, if the flow rate Qf increases and hence the velocity of the flow reaches the velocity V0 in the above equation, then the capability of discharging soil is created. This may be regulated freely by the control of the flow rate Q] of the nozzle. In this case the vanes 38 and 39 have the effect to restrict the flow of fluid within a constant cross-sectional area.

When the capability of the soil discharging mechanism is expressed by volume concentration, the ratio of the excavated soil reaches 20- 30 percent. The experimental data shows that with the soil discharging tube 8 having inner diameter of mm of a block of excavated soil having longer side of 15 cm and shorter side of 10 cm was discharged as it was. This indicates the high capability of the machine.

Referring to FIG. 5, the operation of the excavator of the present invention and its relationship with the facilities required for the operation will now be described.

hereinabove. It may be supported substantially vertically by a turret 2 built at predetermined spot in an installation field. It may be gradually pressed in by the force of a power cylinder 3 and guided by the turret 2 to excave a ditch or bore 6.

The muddy water (stabilizing liquid such as bentnite liquid) is" supplemented, as the excavation work proceeds, from a bentnite mixer S mounted on a muddy water pit 4 arranged near the excavating position, which mixer constantly produced new liquid. The numeral 4a designates a passage interconnecting the excavated ditch 6 and the muddy water pit 4.

The soil discharging tube 8 and the ejecting pipe 7 are piped onto the 'ground as shown, to each of which the suction pump 8a and the ejection pump 7a are con- .nected, respectively. Furthermore, the soil discharging tube 8 is connected with a muddy water separator 9 leaving the suction pump 8a therebetween, which separator separates the excavated soil from the fluid, which, in turn, is passed through a circulating pipe 90 to the ejection pump 74 to circulate water fed from the nozzle and water discharged from the soil discharging tube 8.

The .excavated soil is further passed to a vibrating sieve (not shown) which is a part of the muddy separator 9 and to the circulating pump 9b, thence to a fluid cyclon 9c, and fed to a mixer 9d as solid completely separated from water or fed to the external as the discharging soil. r

The ejection tube 7 and the discharging tube 8 are extended sequentially as the excavation work proceeds. The turret 2 may be movable freely in a horizontal direction to eliminate the work for installing the excavator and simplify repetitive excavating work.

The numeral 10 designates an oil pressure unit which constitutes an operation box for-the excavator of fully oil pressure-driven mechanism as described above. This unit allows all kinds of control.

The second invention relates to an excavation system for deep ditch developedin accordance with the functional features of the novel excavator as described above. This system will now be described below.

As seen from FIG.=.7A, the excavating surface of the excavator in accordance with the first invention is constructed to have a rectangular shape by the slide cutter 30. When the longitudinal and lateral dimensions of the excavating surface of the excavator (these may be considered as the longitudinal and lateral dimensions of the slide cutter 30) are expressed by a X b, and excavation work is started from a point with simple repetition of the work, the number of the repetition being n, then the ditch having the width b and the length n X a may be excavated.

However, as has been well known, when we take the effect of the pressure of the surrounding ground on the excavated ditch in consideration, the effect gradually increases as the ditch becomes deeper and the dimensions (longitudinal and lateral dimensions) of the ditch increase.

In the excavator of the present invention, such disadvantage may be overcome in the following manner.

As shown in FIG. 6, the excavation work of the ditch is effected along a predetermined line in such a manner that a plurality of ditch bores 40 are excavated, each of the bores being spaced from adjacent ones by a constant distance a taking the lateral dimension a of the excavator (of course this may be the longitudinal dimension b instead of a) as a reference, to form discrete bores 40. Thereafter, depending upon the proceeding of the concrete work, the areas 41 left ,unexcavated between the bores 40 and 40 are excavated to complete a continuous ditch 42 having desired length L. Referring to FIG. 6A, when excavation work is effected'in accordance with the present excavation system, excavating a plurality of discrete bores 40 along a predetermined line leaving unexcavated areas 41 of a constant length (a or b) between the bores 40, may be considered to excavate independent, discrete bores of small dimension when viewed one by one, and hence a higher stability for the ground pressure may be assured. It is a particularly remarkable advantage that when the remaining areas 41 left between the bores 40 are to be subsequently excavated, the penetration resistance acting on the excavator 1 reduces remarkably, and, because the rotary cutter rotates in a manner that it collect soil inwardly, as shown in FIG. 6C, the excavation work for the areas 41 may be accomplished without a fear for refilling the excaved bores 40 on pposite sides, resulting in easy and'efficient work. When the work is proceeded in such a manner that individual bores 40 are first excavated along a predetermined line and then depending upon the proceeding of concrete work the ground between the excavated bores 40 are excavated and-discharged, a ditch of the length L (n X a) may be completed simultaneously with excavation of the interleaved area 41. Thus the efficiency of excavating the foundation works can be considerably improved.

Now, let us again discuss about the structure and functions of the excavator explained hereinabove.

The excavator is capable of excavating a ditch of rectangular shape (a X b) with high working accuracy by means of the slide cutter 30 and the rotary cutters l4 and 15. On the other hand, it has a shortcoming as follows: FIGS. 7A and 7B illustrate arrangement of the slide cutter 30 and the rotary cutters l4 and 15, and the hatched portion K at the center of FIG. 7A has poor mechanical excavation ability as seen from FIG. 78, so that the excavated ground has raised portion corresponding to said portion (this, of course, is not desirable).

In order to overcome this disadvantage, the inventor has also developed the following excavating system.

Referring to FIG. 8A, bores 50 each having a diameter which is substantially equal to the width b of the excavator l are previously excavated along a predetermined line, pitch of said bore train being equal to the lateral dimension a (or it may be the longitudinal dimension b) of the excavator. The bores 50 may be excavated by a pre-boring machine or any other machine.

Then, as in the above-mentioned embodiment, a plurality of discrete ditch bores 40 are excavated leaving unexcavated area 41 of the length of a between the bores 50 by using the rotary cutter type excavator I with its center being set to an excavated bore 50 as shown in FIG. 8B, and then, depending upon the proceeding of the concrete work the interleaved areas 41 between the ditch bores 40 are excavated to complete a ditch 42 having the length L (n X a).

excavating work.

As stated hereinabove, the functional feature of the excavator of the present invention to be able to excavate a ditch of rectangular shape with high accuracy makes it possible to realize a unique excavating system to compared with the prior art system.

FIG. 9A, for example, illustrate a case wherein a post of T-shaped cross-section is excavated in situation. In order to accomplish this, ditch bore 61 is excavated to a desired depth with the longitudinal side a of the excavator being oriented horizontally, and after rotating the excavator by 90, another bore is excavated to the desired depth with the side edge of the excavator being precisely placed on the center side wall of the previously excavated bore 61. Thus the T-shaped bore is completed.

By the application of this system, a continuous underground wall which serves as water suppress wall as shown in FIG. 9(8), or ditch bores 64, which are perpendicular to long ditch bores 63 which correspondto outer peripheral structure wall of a conventional building may be excavated with high accuracy.

Also, post bore having cross-shaped cross-section may be excavated in situ as shown in FIG. 9C. In order to accomplish this, two lateral ditches 65 and 65 are excavated leaving an area of the width b therebetween, and then, after the excavator is rotated by 90, the longitudinal ditches 66 and 66, including the interleaved area are excavated to complete the cross-shaped ditch.

All of those excavating systems can be realized by the fact that the excavator of the present invention is capable of excavating a ditch of precise rectangular shape (a X b) with high accuracy.

What is claimed is:

1. An excavator for excavating a ditch comprising a box-type casing of a main frame having its bottom side opened, a pair of rotary cutters mounted at bottom portion of said casing, blades for excavating provided on an outer periphery of cylindrical drum of each of said rotary cutters, a soil discharging tube having a sucking port formed by pressing a central upper portion of cutter casings arranged around said rotary cutters in bell mouth shape, whereby the soil excavated by said cutters and blades and picked up to an intermediate portion of said cutters may be sucked and discharged onto the ground surface through said soil discharging tube.

2. The excavator according to claim 1, further comprising a slide cutter provided on the periphery of said casing and carrying out excavation operation independently from the operation of said casing.

3. The excavator according to claim 2, further comprising upward nozzles mounted just below said sucking port of said soil discharging tube and projectin hi 5 eed 'et flow u wardl t. Hie xcai ator acc rding i o claim 3 including adjustable control means for controlling the flow in said soil discharge tube and said upward nozzles whereby muddy water in a surface ditch communicating with the excavating ditch is maintained in a static state without any variation.

5. An excavator for excavating a ditch comprising a box-type casing of a main frame having its bottom side opened, a pair of rotary cutters mounted at bottom portion of said casing, blades for excavating consisting of sets of leading blades and trailing blades provided on an outer periphery of cylindrical drum of each of said rotary cutters, a driving means transmitting rotating torques of the same speed and the opposite direction from two oil pressure motors through intermediate gear means, said rotary cutters being rotatablydriven by said driving means, a slide cutter provided on the periphery of said casing and having a cutting blade assembly consisting of a leading blade and a trailing blade, power cylinders fixedly mounted at the upper part of said casing, a piston rod of each cylinder being connected with a beam of each slide cutter to permit excavating operation to be carried out following the preceeding rotary cutter, a soil discharging tube having a sucking port and formed by pressing a central upper portion of cutter casings arranged around said rotary cutters in bell mouth shape, upward nozzles mounted just belowsaid sucking port of said soil discharging tube and projecting high speed jet flow upwardly, and ejecting pump connected to said nozzles, whereby the soil excavated by said cutters and blades and picked up to an intermediate portion of said cutters may be sucked and discharged onto the ground surface by said ejecting pump through said discharging tube.

6. A method of excavating using an excavator capable of excavating a rectangular shaped ditch, defined by the longitudinal and lateral dimensions (a Xb) of the excavator by simultaneous rotary and slide cutting a rectangular bore; by repeating the cutting step first to form discrete and alternate rectangular bores each spaced from adjacent bores by a distance equal to the excavating width 0 or b of said excavator and lying along a predetermined line; and by repeating the cutting step secondly to remove the areas of excavating width 0 or b left between said discrete rectangular bores.

7. A method of excavating using an excavator capable of excavating a rectangular shaped ditch defined by the longitudinal and lateral dimensions (a Xb) of the excavator by digging a plurality of first bores whose centers lie along a predetermined line and whose centers are separated by the excavating width a or b of said excavator; by centering said excavator on one of said previously excavatedfirst bores by simultaneous rotary and slide cutting a rectangular bore; by repeating the cutting step on alternate first bores; and by repeating the cutting step on the remainder of said first bores. 

1. An excavator for excavating a ditch comprising a box-type casing of a main frame having its bottom side opened, a pair of rotary cutters mounted at bottom portion of said casing, blades for excavating provided on an outer periphery of cylindrical drum of each of said rotary cutters, a soil discharging tube having a sucking port formed by pressing a central upper portion of cutter casings arranged around said rotary cutters in bell mouth shape, whereby the soil excavated by said cutters and blades and picked up to an intermediate portion of said cutters may be sucked and discharged onto the ground surface through said soil discharging tube.
 2. The excavator according to claim 1, further comprising a slide cutter provided on the periphery of said casing and carrying out excavation operation independently from the operation of said casing.
 3. The excavator according to claim 2, further comprising upward nozzles mounted just below said sucking port of said soil discharging tube and projecting high speed jet flow upwardly.
 4. The excavator according to claim 3 including adjustable control means for controlling the flow in said soil discharge tube and said upward nozzles whereby muddy water in a surface ditch communicating with the excavating ditch is maintained in a static state without any variation.
 5. An excavator for excavating a ditch comprising a box-type casing of a main frame having its bottom side opened, a pair of rotary cutters mounted at bottom portion of said casing, blades for excavating consisting of sets of leading blades and trailing blades provided on an outer periphery of cylindrical drum of each of said rotary cutters, a Driving means transmitting rotating torques of the same speed and the opposite direction from two oil pressure motors through intermediate gear means, said rotary cutters being rotatably driven by said driving means, a slide cutter provided on the periphery of said casing and having a cutting blade assembly consisting of a leading blade and a trailing blade, power cylinders fixedly mounted at the upper part of said casing, a piston rod of each cylinder being connected with a beam of each slide cutter to permit excavating operation to be carried out following the preceeding rotary cutter, a soil discharging tube having a sucking port and formed by pressing a central upper portion of cutter casings arranged around said rotary cutters in bell mouth shape, upward nozzles mounted just below said sucking port of said soil discharging tube and projecting high speed jet flow upwardly, and ejecting pump connected to said nozzles, whereby the soil excavated by said cutters and blades and picked up to an intermediate portion of said cutters may be sucked and discharged onto the ground surface by said ejecting pump through said discharging tube.
 6. A method of excavating using an excavator capable of excavating a rectangular shaped ditch, defined by the longitudinal and lateral dimensions (a X b) of the excavator by simultaneous rotary and slide cutting a rectangular bore; by repeating the cutting step first to form discrete and alternate rectangular bores each spaced from adjacent bores by a distance equal to the excavating width a or b of said excavator and lying along a predetermined line; and by repeating the cutting step secondly to remove the areas of excavating width a or b left between said discrete rectangular bores.
 7. A method of excavating using an excavator capable of excavating a rectangular shaped ditch defined by the longitudinal and lateral dimensions (a X b) of the excavator by digging a plurality of first bores whose centers lie along a predetermined line and whose centers are separated by the excavating width a or b of said excavator; by centering said excavator on one of said previously excavated first bores by simultaneous rotary and slide cutting a rectangular bore; by repeating the cutting step on alternate first bores; and by repeating the cutting step on the remainder of said first bores. 